将字符串复制到剪贴板不起作用（Java）

Question

I'm trying to copy a string to the clipboard once user click on a proper button. This particular operation is supposed to be performed in a JDialog.
Here's part of my code, where the copying should occur:

btnCopy.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {

        StringSelection selection = new StringSelection(txtarContent.getText());
        Clipboard clipboard = Toolkit.getDefaultToolkit().getSystemClipboard();
        clipboard.setContents(selection, selection);

    }
});

I'm using Eclipse (neon.3) on Mac OS X (10.12.4 Sierra).

Edit based on questions in comments:

• No exception is thrown (nor are any errors/warnings)
• After an execution of the code, clipboard remains unmodified

Answer 1

PROBLEM SOLVED:
The problem was not in the solution but in my code.
It seems now that the button's listener wasn't working thus no code was executed.

That's a good lesson for me as a beginner to check even the most obvious things, like whether the listener works or not. Thank you everyone for help.